Due to rapid advance of computer technology and the prevalence of multimedia, the optical disks become more and more important medium for backing up data and information exchange because the former have many advantages including a high storage capacity, easy to handle, and a long preserving time for the stored data. An optical disk drive for operating the disk also becomes more popular for this reason. Presently, most of the desktop computers and notebook computers are provided with at least one disk drive for operating the optical disk. In addition, the disk drive is also employed in many other electronic products, such as DVD player and like.
Conventionally, the disk drive is disposed horizontally in an electronic product. When the disk drive is disposed horizontally, the inserted disk extends perpendicularly to a gravity line. Nevertheless, in recent years, the disk drive in the electronic product is disposed vertically due to its special utility and external appearance. When the disk drive is disposed vertically, the inserted disk extends in a direction parallel with the gravity line. Accordingly, the angle between the rotational axis of a spindle motor and the gravity line can affect the maximum driving force and the balance of the spindle motor. Therefore, varying positions of the disk drive in the electronic product can result in unstable rotation and vibration of the spindle motors. To eliminate the aforesaid unstable rotation problem, an auto-balance system is generally employed so as to lower the vibration of the electronic product, thereby providing a stable balance during the accessing and the track-following operation thereof. Besides, for some other electronic products, the latter can achieve better performance by adjusting their position with respect to the gravity line, such as by turning the display of an LCD device into 90° from its initial position can provide another format of preferred user's interface.
In the past, in order to detect whether the disk drive is assembled vertically or horizontally within an electronic product, the status of _ servo of the pick-up head is computed since the received reflected power can be affected due to the posture of the disk drive. For example, if the disk drive is disposed horizontally, the focusing servo has to provide more current to compensate the weight of the pick-up head. On the other hand, the focusing servo does not have to provide the additional driving current if the drive is disposed vertically. Thus, many logical operation processes and computing data are required to detect the position of the disk drive in the electronic product. Alternately, several complicated mechanical device and electronic switches or specific sensing device must be employed in order to define the gravity direction of the disk drive, thereby complicating the position detecting system.